优化 MarkdownWpfRenderer.cs 中的表格处理逻辑

- 将未使用的循环变量名改为 `_`。
- 使用 `var` 简化 `colIndex` 的类型声明。
- 根据列的对齐方式设置单元格内容的水平对齐。
- 微调代码格式和注释，提高可读性。

src/EleCho.MdViewer/src/EleCho.MdViewer/Markdown/MarkdownWpfRenderer.cs

@@ -192,7 +192,7 @@ public class MarkdownWpfRenderer
         tableElement
             .BindTableBackground();
 
-        foreach (var col in table.ColumnDefinitions)
+        foreach (var _ in table.ColumnDefinitions)
         {
             if (cancellationToken.IsCancellationRequested)
                 return new FrameworkElement();
@@ -200,7 +200,7 @@ public class MarkdownWpfRenderer
             tableContentElement.ColumnDefinitions.Add(
                 new ColumnDefinition()
                 {
-                    Width = GridLength.Auto
+                    Width = GridLength.Auto,
                 });
         }
 
@@ -219,12 +219,12 @@ public class MarkdownWpfRenderer
                     Height = GridLength.Auto
                 });
 
-            int colIndex = 0;
+            var colIndex = 0;
             foreach (var colBlock in row)
             {
                 if (colBlock is not TableCell cell)
                     continue;
-
+                var col = table.ColumnDefinitions[colIndex];
                 Border cellElement = new Border()
                 {
                     Padding = new Thickness(NormalSize / 2, NormalSize / 4, NormalSize / 2, NormalSize / 4)
@@ -236,7 +236,7 @@ public class MarkdownWpfRenderer
                 cellElement.Child = cellContentElement;
                 cellElement
                     .BindTableBorder();
-
+                //block.
                 cellContentElement.Margin = new Thickness(4);
 
                 if (rowIndex % 2 == 1)
@@ -244,6 +244,19 @@ public class MarkdownWpfRenderer
 
                 Grid.SetRow(cellElement, rowIndex);
                 Grid.SetColumn(cellElement, colIndex);
+                if (col.Alignment == TableColumnAlign.Left)
+                {
+                    cellContentElement.HorizontalAlignment = HorizontalAlignment.Left;
+                }
+                else if (col.Alignment == TableColumnAlign.Center)
+                {
+                    cellContentElement.HorizontalAlignment = HorizontalAlignment.Center;
+                }
+                else if (col.Alignment == TableColumnAlign.Right)
+                {
+                    cellContentElement.HorizontalAlignment = HorizontalAlignment.Right;
+                }
+
 
                 tableContentElement.Children.Add(cellElement);